Driveshaft lengths for H55? - Pre '85 truck (1 Viewer)

[Hokie LX]

Hi all,

I just ordered a H55 from my new friend @orangefj45 that just arrived and is sitting in my garage. I’m hoping to get it installed here soon and the last item on my list is driveshafts. My truck is a 1984 so I know I need to lengthen the front shaft and shorten the rear shaft. I am hoping to have driveshafts on hand to install the trans in one go and not wait to install it, measure, and then order shafts. My truck has an OME lift on it but is still spring under and so I believe the standard length 85-87 shafts should fit. Given this is a relatively common mod, I'm hoping someone can help me out.

Can someone measure their front and rear driveshaft lengths on their truck with a H55 installed or a late 85-87 truck, ideally with a lift?

Thanks!

 

[orangefj45]

Thanks for the mention and for ordering the transmission and related parts from us.

The H55F is just under 3.5” longer than the “short” H42 4-speed.
So shortening the rear drive shaft by 3.5” will work out perfect.

Thanks again!

Georg @ Valley Hybrids @ Cruiser Brothers

 

[Hokie LX]

Thanks for the mention and for ordering the transmission and related parts from us.

The H55F is just under 3.5” longer than the “short” H42 4-speed.
So shortening the rear drive shaft by 3.5” will work out perfect.

Thanks again!

Georg @ Valley Hybrids @ Cruiser Brothers

Hi Georg,

Thanks! What about the front shaft?

 

[OSS]

The best way to do it is install the transmission with transfer case first — then the driveshafts when you’re done. That’s how it’s done anyway.
Since it’s step 1 then step 2, you can measure the front driveshaft length needed.
If everything moved back 3.5 inches with the H55, then the front would need to lengthen that distance too.

 

[Hokie LX]

The best way to do it is install the transmission with transfer case first — then the driveshafts when you’re done. That’s how it’s done anyway.
Since it’s step 1 then step 2, you can measure the front driveshaft length needed.
If everything moved back 3.5 inches with the H55, then the front would need to lengthen that distance too.

Definitely agree that locating the trans then measuring is ideal. However, I’d prefer to not have the truck waiting on driveshafts for 10 days before completing the install and since this is a common swap I’m hoping I can get correct lengths ordered ahead of time. Especially since the stock later model 60 shafts work as is. If I can get confirmation on the front shaft length, I can order and have shafts ready when I install the trans.

The h55 is 3.5” longer and Georg stated the rear should be shortened 3.5” to accommodate. However, that would mean the front shaft stays the same since the rear shaft is accommodating the entire 3.5” difference in transmission length yet most posts for h55 into pre-85 trucks state the front shaft needs to be lengthened as well. I just need confirmation of how much the front shaft needs to be lengthened.

My understanding is the h55 is longer but doesn’t necessarily mean it’s an equal 3.5” on each end. Hoping for some clarification.

 

[cruisermatt]

My understanding is the h55 is longer but doesn’t necessarily mean it’s an equal 3.5” on each end. Hoping for some clarification.

Think slower. yes it does. Front DS gets 3.5" longer.

Did you ask a local DS shop about turnaround time? When we do a conversion into a 80-84 60 or FJ62 auto ->manual first thing that gets done is DS's come out and get dropped off, usually they are ready the next day or two days which is the time it takes us to get the Tcase rebuilt, flywheel surfaced, oil pan gasket done, rear main, pedal bucket swapped, etc.
It will likely take you a lot more time then that to rebuild the T-case, do your rear main, pan gasket if you have never done those jobs on a 60 and you are doing it all on the floor on your back vs having done tons of them on a lift. None of it is hard but there is some learning curve to each project.

Did you buy a long-spline input gear? Highly recommend one of those especially with a brand new transmission that you want to last as long as possible

 

[Hokie LX]

Think slower. yes it does. Front DS gets 3.5" longer.

Did you ask a local DS shop about turnaround time? When we do a conversion into a 80-84 60 or FJ62 auto ->manual first thing that gets done is DS's come out and get dropped off, usually they are ready the next day or two days which is the time it takes us to get the Tcase rebuilt, flywheel surfaced, oil pan gasket done, rear main, pedal bucket swapped, etc.
It will likely take you a lot more time then that to rebuild the T-case, do your rear main, pan gasket if you have never done those jobs on a 60 and you are doing it all on the floor on your back vs having done tons of them on a lift. None of it is hard but there is some learning curve to each project.

Did you buy a long-spline input gear? Highly recommend one of those especially with a brand new transmission that you want to last as long as possible

Yup, I got the long-spline input gear at Georg's recommendation. I'm doing the swap at @GLTHFJ60's place so hoping to not have my truck tied up in his garage for a week or longer while waiting on shafts to arrive since I haven't found a local driveshaft shop worth their salt yet to do a quick turnaround and was planning on just ordering some Tom Woods shafts.

Seems I'm still confused on the 3.5" difference in trans length given my truck doesn't have the spacer that the later model trucks did to mimic to the H55 total length.

Making the rear shaft 3.5" shorter and the front 3.5" longer means the total trans/tcase length doesn't change as your making an equal adjustment on both ends.

Since my H42 doesn't have the spacer like the later trucks, there has to be some overall length adjustment that has to be accounted for in the front and rear shaft length that allows for an overall longer trans/tcase combo. So if the rear shaft is shortened 3.5", the front can't also be lengthened an equal amount as that wouldn't allow for a longer trans/tcase.

Am I really just thinking about this all wrong? I am an engineer so that is entirely possible

 

[cruisermatt]

Am I really just thinking about this all wrong? I am an engineer so that is entirely possible

Yes, you are having a rather large lapse in geometric reasoning on this

The transfer case is not getting longer. It’s just moving back 3.5”

 

[cruisermatt]

 

[Zjohnsonua]

Seems I'm still confused on the 3.5" difference in trans length given my truck doesn't have the spacer that the later model trucks did to mimic to the H55 total length.

Making the rear shaft 3.5" shorter and the front 3.5" longer means the total trans/tcase length doesn't change as your making an equal adjustment on both ends.

Since my H42 doesn't have the spacer like the later trucks, there has to be some overall length adjustment that has to be accounted for in the front and rear shaft length that allows for an overall longer trans/tcase combo. So if the rear shaft is shortened 3.5", the front can't also be lengthened an equal amount as that wouldn't allow for a longer trans/tcase.

Am I really just thinking about this all wrong? I am an engineer so that is entirely possible

You're overthinking this one, friend. Analysis paralysis and what not.

The transfer case and its drive flanges are effectively scooting back from your h42 transmission 3.5" when you do this swap. Each driveshaft length has to change respectively.

 

[GLTHFJ60]

Since my H42 doesn't have the spacer like the later trucks, there has to be some overall length adjustment that has to be accounted for in the front and rear shaft length that allows for an overall longer trans/tcase combo. So if the rear shaft is shortened 3.5", the front can't also be lengthened an equal amount as that wouldn't allow for a longer trans/tcase.

EDIT: they already said it. Rear driveshaft shorter by 3.5", front driveshaft longer by 3.5".

 

[Hokie LX]

You're overthinking this one, friend. Analysis paralysis and what not.

The transfer case and its drive flanges are effectively scooting back from your h42 transmission 3.5" when you do this swap. Each driveshaft length has to change respectively.

I see my issue is that I completely and embarrassingly glazed over the fact that the front and rear shafts come out of the tcase and not the front of the trans itself. Geez! That’s a dumb mistake seeing as I’ve taken the shafts out several times lol.

Thanks for explaining it like I’m 5 guys!

 

[cruisermatt]

I see my issue is that I completely and embarrassingly glazed over the fact that the front and rear shafts come out of the tcase and not the front of the trans itself. Geez! That’s a dumb mistake seeing as I’ve taken the shafts out several times lol.

Thanks for explaining it like I’m 5 guys!

Are you going to uwharrie next weekend? We’ll laugh about it over some drinks

 

[Hokie LX]

Are you going to uwharrie next weekend? We’ll laugh about it over some drinks

Yup, I’ll be there! Sounds like a plan

 

[GLTHFJ60]

Are you going to uwharrie next weekend? We’ll laugh about it over some drinks

You mean april 7/8/9?

 

[cruisermatt]

You mean april 7/8/9?

Yeah brooo